JPH03216832A - Magneto-optical recording medium and production thereof - Google Patents

Abstract

PURPOSE:To improve bias characteristics by setting the ratio of the film forming speed and gaseous pressure at the time of forming a recording layer by a sputtering method to a specific value or above. CONSTITUTION:After the inside of a sputtering chamber is evacuated to <=1X10<-6> Torr vacuum degree, an inert gas is introduced into the sputtering chamber. Electric power is then supplied to a target and the target is sputtered under the conditions of >=2.4X10<4> q/p when the film forming speed is designated as q(Angstrom /min) and the gaseous pressure as p(Torr) to form the recording layer essentially consisting of a transition metal and rare earth metal on a substrate. The film forming speed is then slightly increased particularly in the region where the gaseous pressure is low by changing the film forming speed according to the gaseous pressure. A required bias magnetic field is decreased in this way. The improvement in C/N, the miniaturization of the drive and the improvement in the adaptability to overwriting are thus obtained.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for manufacturing a magneto-optical recording medium, and in particular to a magneto-optical recording medium in which bias characteristics are improved by controlling the fluctuation conditions of a recording layer. It concerns the method of obtaining the medium.

[Prior art and its problems]

In recent years, magneto-optical recording media have been widely used for large-capacity data files as magneto-optical disks that can be written and read using laser light.

This magneto-optical recording medium is made by laminating a dielectric protective layer (also called an enhancement layer), a recording layer, an inorganic protective layer, and a thin metal reflective layer on a transparent substrate made of glass, plastic, etc. by sputtering. A configuration having a magneto-optical recording layer with a multilayer structure is widely used because it can obtain a high C/N.

The recording layer for a magneto-optical recording medium with an even higher C/N may be a single layer of an alloy mainly composed of a transition metal and a rare earth metal, or a thin film mainly composed of a transition metal and a thin film mainly composed of a rare earth metal. A layer consisting of more than one layer is used.

In particular, a recording layer using Tb as a rare earth metal and Fe and CO as transition metals has excellent magnetic properties such as rotation angle, and is disclosed in, for example, Japanese Patent Laid-Open No. 7374-A. .

When recording information on a magneto-optical recording medium, first, a bias magnetic field for erasing is applied to the medium and a laser beam is uniformly irradiated, erasing the recorded information that has already been written and at the same time moving the recording layer in a certain direction. Then, recording information is written using a laser beam while applying a bias magnetic field for writing.

The relationship between C/N and the bias magnetic field (Hb) is that generally C/N increases in proportion to the bias magnetic field, but C/N
A saturation bias magnetic field (Hbs) in which the change in Hbs is saturated exists as a characteristic unique to the medium. Reducing this saturation bias magnetic field means that the bias magnetic field necessary for erasing and writing can be reduced, and even if the same bias magnetic field is applied at the same time, the saturation/ζ bias magnetic field is small. It is more advantageous to use the C/N ratio.

The above-mentioned S ear magnetic field (Hb
) is usually 130 to 3000e (oersted), but reducing this value allows the magnet for applying the magnetic field to be made smaller, which is advantageous for miniaturizing the drive.

In addition, magneto-optical recording media have recently become more widely used, and there is a strong demand for overwrite recording, but reducing the bias magnetic field (Hb) required in this case also requires miniaturization of the device and shortening of access time. It is predicted that this will become an essential requirement for shortening the time.

However, no effective method has yet been proposed for reducing the noise magnetic field required during erasing and writing without sacrificing other characteristics such as C/N.

For example, from the viewpoint of the composition of the recording layer, the above-mentioned Tb-Fe-
In a Co-based alloy recording layer, the required bias magnetic field can be considerably reduced by lowering the CO composition ratio and reducing the magnetic moment of the recording layer, but on the other hand, the magneto-optical properties such as the Kerr rotation angle are degraded. It could not be put to practical use.

In addition, from the viewpoint of film formation conditions for the recording layer, there is a method to improve the C/N by reducing the incorporation of impurities and increasing the Kerr rotation angle by lowering the gas pressure during film formation.
However, with this method, the bias characteristics of the recording layer cannot be controlled, and sometimes the sensitivity to external magnetic fields is low, resulting in poor bias characteristics.
Sometimes it became a recording layer.

Another problem with recording layers mainly composed of transition metals and rare earth metals is that they are very easily oxidized and the storage stability of the medium is poor. It is effective to add elements such as Cr, Ta, kl, Pt, and V. r-/Tata No. 11, etc.

However, no technique has been proposed for improving the bias magnetic field in this recording layer.

[Problem that the invention seeks to solve]

The present invention has been made in view of the problems of the prior art, and in particular, the required bias magnetic field (Hb) is relatively lJ.
- It is an object of the present invention to provide a magneto-optical recording medium which is advantageous in improving the C/N ratio, allows miniaturization of the drive, and has excellent O/ζ-write suitability.

Another object of the present invention is to provide a magneto-optical recording medium with excellent storage stability.

[Failure to solve the problem]

The object of the present invention is to control the inside of the sputtering chamber by
After reducing the degree of vacuum to r or less, inert gas is introduced into the sputtering chamber, then power is applied to the target, and when the film formation rate is q (Å/min) and the gas pressure is p (Torr), , q/p is J. 4'X/04 or more, preferably /x/
This is achieved by a method of manufacturing a magneto-optical recording medium 6 in which a recording layer containing transition metals and rare earth metals as main components is formed on a substrate by sputtering under conditions of 0.05 or higher.

According to the manufacturing method of the present invention, by changing the film formation rate according to the gas pressure, especially by making the film formation rate relatively high in a region where the gas pressure is relatively low compared to the conventional sputtering method, the required The bias magnetic field can be made relatively small, and a magneto-optical recording medium can be obtained which is advantageous in improving the C/N and miniaturizing the drive, and is also suitable for overwriting.

In particular, the composition of the recording layer is Tb-Fe-Co-X (X is Cr).
, Ta, A7%Pt, Ti, W, and at least one element selected from
/min) and the gas pressure p in the sputtering chamber, q/p is 1. By setting ≠x704 or more, preferably /X/05 or more, particularly preferably 3X/05 or more, the necessary bias magnetic field is lowered and the corrosion resistance of the recording layer is also improved, resulting in storage stability. A magneto-optical recording medium with excellent properties can also be obtained.

Although the above-mentioned effects of the present invention are not yet clear, by lowering the gas pressure, the structure of the thin film of the recording layer is improved by preventing the incorporation of impurities such as oxygen, moisture, and inert gas molecules remaining in the sputtering chamber. By making the recording layer denser and the crystal grains constituting the recording layer finer, and by increasing the deposition rate relatively, the energy of the sputtered particles increases, so the mixing of the sputtered particles on the substrate progresses and the recorded recording layer is formed. It is presumed that this promotes the densification of the layer, which causes a steep change in coercive force near the Curie point, and that the bias magnetic field acts effectively.

In the method of the present invention, when forming the recording layer, an inert gas such as Ar, Kr, He, etc. is introduced into the sputtering chamber until a predetermined gas pressure p (Torr) is reached to form the recording layer. By adjusting the power applied to each target, which is a metal component, the film formation rate q (Å/
minutes), and q/p is set. A recording layer is formed on a substrate mounted on a substrate holder so that ≠×/04 or more.

The sputtering method in the method of the present invention is preferably a magnetron sputtering method, in which DC [power or RF power is applied to a transition metal target, a rare earth metal target, or an alloy target of these metals to generate plasma of each metal. Then, a recording layer is formed by a one-source simultaneous sputtering method or the like.

The thickness of the recording layer is iooo to 3000k.

Usually, a dielectric layer is deposited between the recording layer and the substrate as a recording layer enhancement layer. Then, an inorganic protective layer for protecting the recording layer is formed on the recording layer.

There are no particular restrictions on the film-forming conditions for the enhancement layer and the protective layer, but the thickness of the enhancement layer is usually 100%.
The thickness of the inorganic protective layer is 200 to 300k.

Furthermore, in order to improve the characteristics of the magneto-optical recording layer, a metal reflective layer can be formed on the inorganic protective layer to a thickness of 300 to OA.

The recording layer obtained by the method of the present invention is a non-quality layer mainly composed of transition metals and rare earth metals, and may be in the form of a single layer or a layer mainly composed of transition metals. It may be a layer in which λ or more layers mainly composed of rare earth metals are laminated alternately.

Further, in order to improve the corrosion resistance of the recording layer, Cr
It is preferable to contain %Ta, A4, Pt1Ti, W and V, among which Cr is the most effective.

The content thereof is from 1 to 20 atL%, preferably from 3 to 1/jat%.

As the transition metal, for example, Fe, Co, Ni, etc. can be used, and as the rare earth metal, Tb, Gd, Sb, DY, Sm, etc. can be used. Specific examples of the composition of the recording layer include (}dCo, GdFe.TbFe, DyFe, Gd
FeTb, TbFeCo, TbFeNi, GdFeCo
etc. Among them, TbFeCo is the most preferred, and its composition further includes Cr, Ti, W, Ta, A7, Pt.
A composition containing V and V is preferable in terms of having practically sufficient corrosion resistance.

As the material for the enhanne layer and the inorganic protective layer, for example, dielectrics such as oxides such as SiOx, SiNx, AJNx, and Zn8, nitrides, and sulfides are used. Among them, from the viewpoint of optical properties and protective functions, Si nitride,
A7 nitrides or mixtures thereof are preferred.

Further, a metal reflective layer is provided on the inorganic protective layer, and further C
/N can also be improved. The material of the metal reflective layer is 300 to 300 mm, mainly made of AJ or Ni.
It is a thin metal film with a thickness of

Polycarbonate, polymethyl methacrylate, epoxy resin, glass, etc. are used as the material for the substrate in the magneto-optical recording medium and its manufacturing method of the present invention. Among them, polycarbonate, polymethyl methacrylate,
A resin substrate such as epoxy resin is preferred, and polycarbonate is particularly preferred since it has advantages such as low water absorption and high glass transition transfer.

In the magneto-optical recording medium of the present invention, after forming a magneto-optical recording layer by forming each layer on a substrate as described above, the top surface and side surfaces thereof are coated with an organic resin protective layer such as an ultraviolet curing resin. It is also possible to further improve the storage stability of the magneto-optical recording medium.

Furthermore, a double-sided recording type magneto-optical recording medium can be obtained by bonding the substrates with the inner surfaces of the magneto-optical recording layers facing outward via an adhesive layer made of a hot melt adhesive or the like.

〔Effect of the invention〕

The deposition rate q (Å/
minute) to the gas pressure p (Torr), q/p is 2. ≠
By setting the ratio to be ×/04 or more, a magneto-optical recording medium with excellent bias characteristics can be obtained.

The novel features of the present invention will be explained in more detail with reference to the following Examples and Comparative Examples.

(Example 1l) Diameter lsommm with guide groove provided on one side by injection molding
．． thickness/ . A 2 mm polycarbonate substrate was set on a rotating substrate holder of a sputtering device, and argon gas was introduced into the sputtering chamber to set the gas pressure to /mTorr. Then, using the magnetron scattering method K, a thin film of SiNx with a thickness of 11OOA was first formed as an enhancement layer.

Next, a power of 700 W was applied to the FeCoCr alloy target, and a power of λtoW was applied to the Tb target to reduce the film formation rate coj! A recording layer having a composition of Tb16Fe68CogCr6 was formed on the substrate by dual sputtering at a rate of .ANG./min to a thickness of .lambda.OA.

The gas pressure p during film formation of this recording layer can be determined by controlling the flow rate of argon gas introduced into the film formation chamber.
×/0 4 Torr.

Note that the distance between the target and the substrate is /lfO
mm.

After that, 8iN was applied as an inorganic protective layer on the recording layer.
A thin film of x is formed with a thickness of 23 OA, and a thin film of AJ alloy is further formed with a thickness of aOoA as a metal reflective layer on top of it, to form a magneto-optical recording layer with a μ layer structure on the substrate. A sample of a magneto-optical recording medium was obtained.

(Examples-2 to -2 and Comparative Examples-1 and 1) Example 1
In , a magneto-optical film with the same composition and structure was prepared under the same conditions as in Example 1/, except that the gas pressure p during recording layer deposition and the recording layer deposition rate q were changed as shown in Table 1. A sample of the recording medium was obtained.

(Example-lo) Diameter lJOmm with guide groove provided on one side by injection molding
A polycarbonate substrate having a thickness of 1 mm and a thickness of 1 mm was set on a rotating substrate holder of a sputtering apparatus, and argon gas was introduced into the sputtering chamber to set the gas pressure to /mTorr. Then, by magnetron sputtering method, firstly, enno.
A thin film of 8iNx with a thickness of //00A was deposited as a conductive layer.

Next, a power of 31 IOW was applied to the FeCO alloy target, a power of /2jW was applied to the Tb target, and binary simultaneous snow ξ ivy was performed at a film formation rate of iioÅ/min to form a film on the substrate. The composition is TbH3Fe8Co74. 24! A recording layer having a thickness of OA was deposited.

Note that the distance between the substrate and the target is /fOm
It was set as m.

The gas pressure p during film formation of this recording layer can be adjusted by controlling the flow rate of argon gas introduced into the film formation chamber.
．． 4L×/0 3 Torr.

After that, an inorganic protective layer of SiN is formed on the recording layer.
A thin film of x is formed with a thickness of cojOA, and a thin film of 1 alloy is formed as a metal reflective layer on top of it with a thickness of ≠OOOA to form a magneto-optical recording layer with a q-layer configuration on the substrate. A sample of a magneto-optical recording medium was obtained.

(Examples -//~-/t, and Comparative Example-3, Kazuhiro) In Example 1/O, the gas pressure p and recording layer deposition rate q during recording layer deposition were as shown in Table 7. Example 1i except for the changes
A sample of a magneto-optical recording medium having the same composition and structure was obtained under the same conditions as in Example 3.

The strength of the saturation bias magnetic field (Hbs) of the sample of the magneto-optical recording medium obtained as described above was measured under the following conditions.

Measurement of saturation bias magnetic field (Hbs): For the samples of the magneto-optical recording media of the above examples and comparative examples, a bias magnetic field of toooe (Oersted) was applied to the magneto-optical recording layer at a recording power of 3 to 1 mW at ξ watts. Perform writing, find the optimal recording/g power that maximizes C/N, and then set the bias magnetic field at the optimal recording power from 0 to 7 oo.
Obtain a curve representing the change in C/N with respect to the bias magnetic field by varying it within the range of Oe (Oersted), and change the bias magnetic field corresponding to the C/N that is /dB lower than the saturation C/N read from the curve to the saturation bias magnetic field ( Hbs).

Table 1 shows the measurement results obtained.

Claims (2)

[Claims] (1) After setting the sputtering chamber to a vacuum level of 1×10^-^6 Torr or less, inert gas was introduced into the sputtering chamber, and then power was applied to the target to reduce the film formation rate to q(Å).
/min) and gas pressure p (Torr), q/
A method for manufacturing a magneto-optical recording medium, comprising forming a recording layer made of a transition metal and a rare earth metal on a substrate by performing sputtering under conditions where p is 2.4×/10^4 or more. (2) In a magneto-optical recording medium having a recording layer mainly composed of transition metals and rare earth metals formed on a substrate by sputtering, the recording layer is made of Tb-Fe-Co-X (X is Cr). , Ta, Al, Pt
, at least one element selected from Ti, W, and V), and when the film formation rate is q (Å/min) and the gas pressure is p (Torr), q 1. A magneto-optical recording medium characterized in that the film is formed under conditions where /p is 10^5 or more.